Apparatus and method for controlled fluid cooling during laser based dental treatments

ABSTRACT

A system for dental tissue treatment includes a system for directing a laser beam to an area of dental tissue to be treated, and a fluid-delivery system for directing and controlling a flow of a fluid. The fluid is directed to at least a portion of the area to be treated and the fluid flow is controlled to substantially prevent both a change in laser energy absorption by the dental tissue and attenuation of treatment efficiency due to fluid interference with the laser beam. The fluid present in at least a portion of the area to be treated may prevent or reduce the likelihood of melting of enamel in that area.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to and claims the benefit of priority toU.S. Provisional Patent Application Ser. No., 61/646,579 filed on May14, 2012, the entirety of which is hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to coolant systems and in particular to coolantsystems for laser-based dental treatment.

BACKGROUND

Some dental treatment systems use lasers, e.g., for cutting toothenamel. It may be beneficial to replace drills conventionally used indental treatment with laser-based systems, in part because lasers canprovide for better control of the process of cutting and removingmaterial from a tissue to be treated, such as a tooth. Also, laser-basedsystems are typically less noisy and may produce less vibrations than aconventional drill. Lasers have also been found to be useful in theremoval of dental material with less amount of local anesthetic thanthat required when the procedure is performed with a drill. For thesereasons many in the dental industry have expected for some time thatlaser based systems will replace the drill based dental treatmentsystems.

The Food and Drug Administration (FDA) has approved seven differenttypes of lasers and laser diodes for use in dental applications. Lasersused to treat soft tissue are chosen according to the water absorptioncharacteristics of the laser, and various other characteristics so thatthe blood is cauterized and bleeding is minimized. Many of the dentaltreatment systems, however, cut the enamel or hard tissue using lasersthat exhibit high water absorption. Typically, the applied laser energyis absorbed in water in tooth enamel (about 4% by volume), causing thewater to vaporize, and the resulting steam causing to facture the hardtissue/enamel and thus removing a portion of the enamel from the tooth.Because the laser wavelength is chosen such that a significant portionof the laser energy is strongly absorbed by water, a common problem withsuch systems is that the cutting operation is slow, due to the lowpercentage of water in the enamel. In fact, this method of removingdental hard tissue is often considerably slower than using dental drillsand many dental procedures are completed in less time by anoperator/dentist using a conventional drill than by using a laser thatoperates by absorption of laser energy in water. For this reason maypractitioners choose not to use laser based systems for dentaltreatment, and as such the benefits that laser based treatment can offerare not widely available at present.

Laser wavelengths in the range of 5 to 15 μm are strongly absorbed bythe hydroxyapatite that makes up to about 96% of tooth enamel by weight.Therefore, using lasers in the range of about 5 μm up to about 15 μm canresult in faster cutting of hard tissue than that using known laserbased dental treatment systems. As explained below, cooling isparticularly important in using lasers in the 5 to 15 μm range.

The use of a fluid to assist in cleaning during cutting, e.g., forremoving particles created during the cutting operation is known. Suchfluids may also be used for cleaning prior to and following the cuttingoperation. In general in laser-based dentistry, without adequate coolingenamel melts when ablated by a laser of any wavelength, formingnon-apatite CaP phases. Therefore, when a laser is used for cutting, afluid can be used to cool the tissue within the treatment area and/orthe surrounding area, to prevent thermal damage thereto, in addition tocleaning.

When the laser is used to fracture the tooth structure by watervaporization, water provided by the system to cool the treatment areacan interfere with the laser beam without a significant reduction inmaterial removal rates. This is because the coolant, that may absorb thelaser radiation and vaporize can serve to remove hard tissue material byimparting disruptive forces to the treatment area. In some systems, thecoolant system is intentionally configured such that the coolantinterferes with the laser beam to impart disruptive forces on dentalhard tissue. In some laser based dental treatment systems, the coolantis provided only to avoid or minimize the melting of the enamel, withoutregard to whether the coolant interferes with the ablation operation ofthe laser beam. Some systems that deliver coolant between laser pulsesdo not provide forced convective cooling from the surface of the dentalregion being treated at or nearly at the time the surface is beingheated. This can cause the treated surface to experience thermal cycles,heating during laser pulses and cooling in between such pulses.

A dental laser system in which ablation occurs, at least in part, due toabsorption of the laser energy in the hydroxyapatite of the hard tissueis likely to experience a marked reduction in material removal rate whena cooling fluid interferes with the laser. In such systems, providingunregulated quantities of water or other coolants is often not abeneficial solution to solve the problem of the melting of the enamel.This is because hydroxyapatite absorbs laser energy at 9.3 to 9.6 μm(which can be classified mid to far infrared range of the laserwavelength) but water also absorbs laser energy at 9.3 to 9.6 μm, and assuch, the cooling fluid may significantly attenuate the laser power usedfor ablation. Therefore, an excess amount of water can interfere withthe cutting operation of the laser beam.

In addition, though the melting of the enamel can decrease theefficiency of cutting in general, this problem can be significant whenmid to far infrared lasers are used. This is predominantly because theCaP phase structure has a completely different absorption characteristicthan hydroxyapatite such that far-infrared 9.3-9.6 μm energy goes frombeing highly absorbed to virtually not absorbed in the CaP phases.Therefore, this shift in absorption mechanism can make the cooling andablation of enamel at mid to far-infrared wavelengths far more criticalthan near-infrared (e.g., conventional) wavelengths where the absorptionmechanism is water. Because the ablation of the hydroxyapatite andnon-apatite CaP phases is not that dissimilar, some enamel melting thatcan be tolerated when cutting with near infrared (conventional) laserenergy, because the ablation is generally caused by evaporated water. Itis highly desirable to avoid such melting when mid to far infraredenergy laser is used for ablation because the CaP phases cansubstantially mitigate or even prevent absorption of the laser energy inthe hard tissue to be removed.

As such, there is a need for improved systems and methods to control thefluid used to cool the tissue during laser processing thereof to providefor sufficient removal rates while substantially preventing melting ofthe enamel.

SUMMARY OF THE INVENTION

In various embodiments, a system and a method in accordance with thepresent invention facilitates effective dental treatment in which therisk of melting of the enamel by a laser beam is mitigated or eliminatedwithout significantly impacting the efficiency of cutting the dentaltissue. This is achieved, in part, by regulating the flow of a coolantfluid such that an amount of fluid present in the treatment area isadequate to minimize the risk of melting of the enamel, but is not soexcessive as to interfere with the laser beam by absorbing a significantportion of the laser energy. Specifically, because molten enamel cancover hydroxyapatite, and thus substantially prevent absorption of thelaser energy thereby, the system and method ensure that an amount ofwater/coolant that is sufficient to inhibit or minimize melting of theenamel is present in the treatment area. The amount of water/coolant isminimized, however, so that the portion of radiation absorbed into thewater/coolant is minimized and absorption of the laser energy by thehydroxyapatite/enamel to be removed is maximized or maintained near thepeak absorption. As a result, the portion of the generated laser energythat is utilized for ablation can be maximized so that the cost and/orduration of the mid to far-infrared laser based treatment is minimized,while preventing melting of the enamel. As part of regulating the flowof the coolant fluid, both the location and amount of cooling fluid maybe controlled. Various embodiments may also employ computer controlledlaser beam delivery.

Often, as ablation by a laser progresses, a hole or depression forms inthe treatment area (surface of the tooth, hard tissue, etc.). Therefore,it is beneficial that the coolant fluid spray is formed such that thecoolant fluid wets the surface exposed by ablation, to ensure enamelmelting does not occur therein, and non-apatite CaP phases are notformed over the exposed surface. It must also be ensured, however, thatcoolant fluid pooling is avoided. The coolant fluid pooling may lead toincreased absorption of laser energy in the pooled coolant fluid andcorrespondingly decreased hydroxyapatite ablation rates. Moreover,interaction of water (coolant fluid in general) with the infrared laserbeam prior to impingement thereof on the enamel surface can lead toadditional absorption of the laser energy in the water, and even lesshydroxyapatite absorption. Therefore it is advantageous to ensure thatas little coolant spray or mist as possible interacts or intersects withthe infrared laser light delivered to the treatment area.

Accordingly, in one aspect, various embodiments feature an apparatus fordental tissue treatment. The apparatus includes a system for directing alaser beam to an area of dental tissue to be treated. The apparatus alsoincludes a fluid-delivery system for directing and controlling a flow ofa fluid to at least a portion of the area to be treated to substantiallyprevent both a change in laser energy absorption by the dental tissueand attenuation of treatment efficiency due to fluid interference withthe laser beam. The fluid delivered to at least a portion of the area tobe treated may prevent melting of enamel in that area, or maysignificantly reduce the risk of such melting.

In some embodiments, the fluid includes a liquid and a gas, and thefluid-delivery system may be configured to adjust a proportion of avolume of the liquid with respect to a volume of the fluid. The liquidmay include or consist essentially of water. Alternatively, or inaddition, the liquid may include one or more of a salt, a peroxide, amedication, a pigment, a mineral, a cutting chemical, and a surfactant.The gas may include or consist essentially of air.

In some embodiments, the fluid-delivery system controls (e.g., using avalve) the flow of the fluid. The fluid-delivery system may beconfigured to provide a sufficient amount of fluid to substantiallyprevent the melting of the dental tissue. The fluid-delivery system mayalso be configured to limit an amount of fluid delivered to thetreatment area to limit absorption of the laser beam energy in thefluid.

The fluid may include or consist essentially of a liquid, and thefluid-delivery system may be configured (e.g., using a valve) to adjusta rate of flow of the liquid. In some embodiments, the fluid-deliverysystem is configured to adjust a pressure of the liquid flow in therange from about 0 psi up to about 40 psi. The fluid-delivery system mayalso be configured to switch the liquid flow on and off, so as todeliver a liquid burst or a series of bursts. The frequency of switchingmay be up to about 10 Hz, and a duration of one liquid burst may be upto about 1000 milliseconds.

In some embodiments, the fluid includes or consists essentially of agas, and the fluid-delivery system (e.g., a valve) is configured toadjust a rate of flow of the gas. Alternatively or in addition, thefluid-delivery system may be configured to adjust a pressure of the gasflow in the range from about 0 psi up to about 80 psi. Thefluid-delivery system may be configured to switch the gas flow on andoff, so as to deliver a gas burst. A gas burst may be deliveredalternately with the delivery of a liquid droplet or burst such that theliquid may provide cooling, and the gas burst removes any excess amountof liquid, that may interfere with the laser beam, from the treatmentarea/region. The frequency of switching may be up to about 10 Hz, and aduration of one gas burst can be up to about 1000 milliseconds.

In some embodiments, the fluid-delivery system is configured (e.g.,using a valve) to adjust a rate of flow of the fluid. For example, thefluid-delivery system may be configured to adjust a pressure of thefluid flow in a range from about 0 psi up to about 80 psi. In someembodiments, two valves may be used—one to control/regulate the flow ofa liquid and a second valve to control/regulate the flow of a gas, theliquid and the gas forming the coolant fluid.

In some embodiments, the fluid-delivery system includes a pressurerelief regulator for controlling the flow of the fluid, and the fluidincludes a gas. The pressure relief regulator may be configured toadjust a pressure of the gas flow in the range from about 0 psi up toabout 80 psi. In some embodiments, the pressure relief regulator isconfigured to adjust a pressure of the gas flow in one or more of arange from about 0 psi up to about 5 psi, causing the fluid to form adroplet at delivery, a range from about 5 psi up to about 15 psi,causing the fluid to form a column at delivery, and a range from about15 psi up to about 80 psi, causing the fluid to form a mist at delivery.

The fluid-delivery system may include a positive displacement pump forcontrolling the flow of the fluid, and the fluid may include or consistessentially of a liquid. The positive displacement pump may include aperistaltic pump. The positive displacement pump may operate at afrequency of up to about 750 rpm, and the frequency of the pump cancontrol a rate of flow of the liquid. In some embodiments, the fluiddelivery system includes a fluid flow switch that can detect thepresence of the fluid flow and/or the presence of bubbles in the fluidflow. The fluid flow switch may be adapted to control the laser beam ifa lack of fluid flow is detected and/or a fluid flow including bubblesis detected.

In some embodiments, the fluid-delivery system includes a nozzle formingone or more orifices. The nozzle may form a number of orifices. Forexample, the nozzle may form up to 10 orifices. Each orifice of theseveral orifices may have a diameter in a range from about 0.008 inchesup to about 0.15 inches. The several orifices may be configured in apolygonal pattern, a circular pattern, or an arcuate pattern. In someembodiments, an orientation of the nozzle with respect to an axis of thelaser beam is adjustable, for example, at an angle in a range from about0° up to about 90° with respect to the laser beam. In some embodiments,the orientation of the nozzle is about 77° with respect to the laserbeam.

In some embodiments, a distance between a tip of the nozzle and the areaof the dental tissue to be treated is in the range from about 2millimeters up to about 50 millimeters. The fluid-delivery system may beconfigured to direct the fluid flow as one or more of a series ofdroplets, a series of columns, and a mist. The area to be treated may bein a range from about 0.00005 square inches up to about 0.055 squareinches, and the dental tissue may include or consist essentially of ahard dental tissue. In some embodiments, an air curtain eliminates orreduces the risk that the cooling fluid after striking the area/regionto be treated (e.g., a surface of a tooth) may bounces back andinterfere with the laser beam.

In another aspect, various embodiments feature a method for dentaltissue treatment. The method includes directing a laser beam to an areaof dental tissue to be treated, and directing and controlling a flow ofa fluid to at least a portion of the area to be treated to substantiallyprevent both a change in laser energy absorption by the dental tissueand attenuation of treatment efficiency due to fluid interference withthe laser beam.

The flow of the fluid may be controlled. In some embodiments, the methodincludes controlling the flow of the fluid so as to provide a sufficientamount of fluid to substantially prevent the melting of the dentaltissue. The control of the fluid flow may also include limiting anamount of fluid to limit absorption of the laser beam in the fluid.

In some embodiments, the control of the flow of the fluid is performed,at least in part, by using a pressure relief regulator. The method mayinclude pumping the fluid using a positive displacement pump so as tocontrol the fluid flow. In some embodiments, the method includesmonitoring the flow of the liquid using a fluid flow switch, andcontrolling the laser beam if a lack of fluid flow is detected and/or afluid flow that includes bubbles is detected. The fluid may be deliveredusing a nozzle forming one or more orifices. An orientation of thenozzle with respect to an axis of the laser beam may be adjusted todirect the coolant fluid to a selected spot within the area oftreatment. A hard dental tissue may be treated in some embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more apparent in view of the attacheddrawings and accompanying detailed description. The embodiments depictedtherein are provided by way of example, not by way of limitation,wherein like reference numerals refer to the same or similar elements.The drawings are not necessarily to scale, emphasis instead being placedupon illustrating aspects of the invention. In the drawings:

FIG. 1 show a cross sectional view of a tooth and an exemplary processof supplying a cooling fluid via a fluid delivery system according toone embodiment;

FIG. 2 shows another cross sectional view of the tooth as the cuttingprocess continues creating a controlled cut profile, according to oneembodiment;

FIG. 3 shows a plan view of a section of the tooth with a square cutregion and delivery of the coolant fluid to the cut region, according toone embodiment;

FIGS. 4A-4D depict various exemplary nozzles, according to differentembodiments;

FIG. 5 is a table of various parameters used to control the fluid flowaccording to various embodiments;

FIG. 6 schematically depicts a fluid delivery system in which the fluidincludes both a liquid and a gas, according to on embodiment;

FIG. 7 depicts a relationship between volumetric flow rate of a coolantand hard tissue removal rate, according to one embodiment.

DETAILED DESCRIPTION

A process is disclosed that combines a laser based dental treatmentsystem with a controlled delivery of cooling fluid. The laser basedsystem may be computer controlled and the coolant fluid delivery systemmay include an air curtain to limit the amount of cooling fluid thatcould interfere with the laser beam.

FIG. 1 depicts one embodiment in which a laser beam 1 emerges from ahand piece 2, which is a part of the laser treatment/cutting system 3.The laser beam can be computer controlled, and is reflected off a mirror4 to perform the cutting operation on the tooth 5 or other tissue Theuser can select the geometry of the cut 6 and the depth of the cut 6.Cooling fluid 7 is directed to the tooth 5 via nozzles 8 and 9. Thisfluid provides both the critical cooling needed to fully control thecutting but also helps to remove the cut material from the tooth 5. Aseparate nozzle assembly 10 supplies an air curtain 11 that may keep thecooling fluid from splashing back into the hand piece 2. The separatenozzle assembly 10 is designed to supply a controlled amount of air toform the air curtain 11 that is substantially a laminar flow. This canminimize the disruption to the laser beam 1. The flow of the coolantfluid is generally controlled such that the cuts, such as cut 6, can beachieved consistently and in a repeatable manner using the laser beam 1.

FIG. 2 depicts a section of the tooth 5 when the cut 6 is in progress.The laser beam 1 is focused on only a portion of the cut 6 and isscanned to achieve the final geometry and depth of that cut 6. The fluidflows 7, 12 are delivered from nozzles 9, 8 respectively and aredirected and controlled by the design of the nozzles 9, 8. Inparticular, the aperture size of the nozzles and their orientation areselected according to one or more of the parameters shown in FIG. 5. Theorientation of the nozzles can determine the angle at which the fluidspray from the nozzle impinges a dental surface to be treated.

In some embodiments, the flows 7, 12 of the cooling fluid are controlleddifferently as the cut 6 gets deeper. It is beneficial to provide anadequate amount of cooling fluid from the flows 7, 12 to the bottom ofthe cut 6, so as to substantially prevent melting of the enamel at thebottom. As the cut 6 becomes deep, this can be accomplished by changingthe flow pattern from droplet or mist, which may be suitable when thetreatment region is generally flat, to a fluid column when the cut isdeep. The flow pattern may be changed by varying the pressure of thegaseous fluid. Generally, lower gas pressures provide a droplet flowpattern, slightly higher gas pressures provide a column of coolant, andhigher gas pressures provide a mist, with the highest gas pressuresproviding the finest mist. Varying the gas pressure may be computercontrolled through the use of an electric regulator, for example an SMCITV-0030-3UBS electric regulator. Pooling of the coolant fluid at thebottom of the cut 6 can be avoided, however. This can be achieved, inpart, by delivering the column of fluid intermittently, such as in apulsed pattern. In addition or alternatively, a droplet or a beam of acoolant liquid and a bust of a gas (such as air) can be alternatelydelivered to the cut 6, so as to provide adequate wetting and coolingwhile minimizing or avoiding pooling of the liquid.

FIG. 3 shows a view looking down on a surface of the tooth 5 with thesquare cut 6. In order to sufficiently cool the entire cut region 6, thecoolant flow 13 can be delivered in a uniform manner (e.g., with avariation of the amount of fluid delivered during at least a part of thetreatment less than 2%, 5%, 15%, etc.) throughout the geometry of thecut 6. This can be achieved, in part, by delivering the coolant fluid asa mist, or by delivering the coolant via different orifices of thenozzle at different times, to target different locations 15, 16, 17 ofthe cut region 6. In order to target different locations multiple fluidconduits may fluidically connect different nozzles with a single pumpvia different switching valves, or different nozzles may be in fluidiccommunication with a corresponding pump in a set of pumps.

FIGS. 4A-4C show a cross-section of a typical 5-15 μm dental laserhand-piece, and a cross-sections of two exemplary nozzles, respectively.The hand-piece 3 encloses the beam path 2 and the 45 degree turningmirror 4. The nozzle assembly 10 is inserted into the hand-piece 3 andthe cross-section shows typical misting nozzles 8, 9. Fluid, i.e., aliquid, a gas, or a mixture thereof can be delivered through the nozzles8, 9. In some embodiments, liquid (e.g., water) may be delivered throughone nozzle (e.g., nozzle 8) and a gas (e.g., air) may be deliveredthrough the other nozzle (e.g., nozzle 9). As depicted in FIG. 4B, thenozzle assembly has two orifices in a rim. The nozzle assembly depictedin FIG. 4C has four orifices. In general, a nozzle assembly may have asfew as one orifice and more than four (e.g., 6, 8, 10, etc.) orifices,so as to control one or more individual fluid flows and/or the fluidflow resulting from the combination of the flows through each orifice.FIG. 4D depicts an embodiment of a nozzle assembly 50 that includes anozzle 52 oriented at an angle of about 77° with respect to an axis ofthe laser beam 54. The nozzle assembly 50 includes another nozzle 56oriented at an angle of about 30° with respect to the axis of the laserbeam 54. A controller may select the coolant fluid flow via the nozzle52 at one time during a dental treatment and via the nozzle 56 atanother time during the dental treatment. Even though the nozzleassembly 50 includes only two nozzles, this is illustrative only. Ingeneral, a nozzle assembly may include more than two nozzles, each ofwhich or groups of which are oriented at different angles with respectto the axis of the laser beam. Each nozzle or groups of nozzles may beselected to deliver the coolant flow at different times during thedental treatment.

Various parameters of the system, e.g., pressure and flow rate of a gasand a liquid that may be combined in a nozzle to form a mist, a droplet,or a column, may be adjusted and controlled during the treatment. Thevarious parameters used to control the fluid flow are depicted in FIG.5. The cooling fluid may further be treated with surfactants or otherchemicals that are safe for use in dental treatment, and that canenhance the removal of enamel and/or assist in maintaining a thinuniform layer of the cooling fluid in the area of the cut.

FIG. 6 schematically illustrates a fluid delivery system that providesfluids to the laser treatment area. The liquid fluid is stored in avented reservoir 16. The treatment system is notified when liquidcoolant is low, by a liquid level switch 18. An example of a suitableliquid level switch is the pairing of a magnetic float, such as MEDERItem No: 2500000026 within the reservoir and a normally open reedswitch, such as MEDER Item No: 2242711054 that closes when the float isproximate (e.g., in contact with or within a few millimeters from thereed switch). Coolant/water is pumped from the vented reservoir 16,using a positive displacement pump 20. The use of the positivedisplacement pump 20 allows for control of the liquid fluid flow rate asthat rate is generally proportional to the rotational velocity of thepump 20. In general, the higher the rotational velocity of the positivedisplacement pump 20 the greater the flow rate of the liquid fluid andthe greater the quantity of the liquid fluid delivered to the treatmentarea.

A peristaltic pump is an example of a positive displacement pump that iswell suited for a fluid delivery system, because the wetted surfaces ofthe pump are usually limited to a tube within the pump. An FDA complianttubing may be used within the peristaltic pump. An example of aperistaltic pump that is suitable for a fluid delivery system is a Boxer9000 paired with a 375 rpm motor and 2 mm I.D. PharMed BPT biocompatibletubing. Because the flow of liquid fluid is needed to sufficiently coolthe treatment area and to substantially prevent melting and thermaldamage of the hard tissue, a fluid flow switch 22 can be used to ensurea flow of the liquid fluid to the treatment area. The Sensirion LG01 isan exemplary flow switch used in the system illustrated with referenceto FIG. 6. In addition to detecting the liquid fluid flow the switch 22can also detect the presence of bubbles that could potentially causeintermittent misting or delivery of the liquid fluid. If complete and/orpartial interruption (e.g., due to a large number of bubbles) isdetected in the liquid flow, the operation of the laser beam can beturned off manually and/or automatically to prevent any damage to thetreatment area.

The coolant fluid in the exemplary system shown in FIG. 6 also includesa gas, which is air in one embodiment. In general, the coolant fluid maynot include any gas, or may include gases other than air. An aircompressor 24 supplies the air. A compressor that is small enough sothat it can be positioned inside the housing for the laser device canprovide sufficient pressure and flow. Additionally or in thealternative, an external air compressor may be used with the fluiddelivery system. The Gardner Denver Thomas 415ZC36/24 is an exemplaryair compressor. The air may be filtered and dried using an air filter 26such as the SMC AF20-NO2C-CZ air filter with automatic drain.

The pressure of the air is regulated by using a pressure reliefregulator 28. By changing the pressure of the gaseous fluid, the liquidfluid may be jetted in the form of a droplet at very low or low gaspressure (e.g., from about 0 psi up to about 5 psi), a column at low ormedium gas pressure (e.g., from about 5 psi up to about 15 psi), or mistat high gas pressure (e.g., from about 15 psi up to about 80 psi). Theaeration of the mist can be further controlled by the regulated pressureof the gaseous fluid, such that the higher the gas pressure the finerthe mist. The SMC NARM1000-2A1-N01G is an exemplary air regulatorsuitable for some embodiments of the fluid delivery system.

In the system shown in FIG. 6, the gas pressure at the nozzle orifices36 is controlled by a normally closed solenoid valve 30, e.g., the SMCVQZ115-5L1-01T valve. By opening this valve, air is supplied to thenozzle 10 to form a mist. Providing a regulated air pressure to the mistnozzle along with a regulated flow of liquid coolant can produce a jetof aerated coolant that has repeatable flow, form, and coolingproperties. For example, an air pressure around 20 gauge psi can providea uniform mist over a broad range of water flow rates. A water flow rateof about 6.9 ml/min can provide sufficient cooling for many hard tissuedental treatments with moderate laser power. The water flow rate may bereduced to as low as about 2 ml/min and increased to as high as about 10ml/min by the operator (e.g. a dentist) to achieve a high quality cut.The change in water flow rate can be made independently of the airpressure setting. Generally, low water flow rates may be used fortreatment of pulp, dentin, or soft tissue because the laser is typicallyoperated at less power than that used to cut hard tissue and, as such,the need for cooling will be less. High water flow rates may begenerally used with laser power at a high setting, for the treatment ofhard tissue such as enamel. The greater the water flow rate the greaterthe cooling of the treatment area/region.

The laser system can ensure that gas/air pressure is present in thenozzle 10 when the solenoid valve 30 is open by monitoring the gas/airflow with a pressure switch 32 located on the opposite side of thesolenoid valve 30 than the side on which the compressor 24 is located.The pressure switch, 32, (e.g., the SMC PS 1000-R07L) may indicate tothe laser system whether the air pressure is above a set threshold. Ifthe air pressure is below a certain specified threshold, the lasersystem may be shut down manually and/or automatically.

In the fluid delivery system depicted in FIG. 6, the gas (e.g., air) andliquid fluid (e.g., water) are combined in a mixing chamber 34 in themisting nozzle head and then jetted out of one or more orifices 36. Inthe embodiments that use more than one orifice, smaller more restrictiveorifices can provide a more evenly distributed mist. The fluid deliverysystem may include an independent controller or may be controlled by thelaser system controller.

Various embodiments of a system and method described above may use alaser that has a wavelength between about 5 and 15 μm and that candirectly interact with a major constituent of the tooth enamel therebycutting that enamel rapidly and with smaller energy pulses compared tothe lasers conventionally used in dental treatment, allowing moreprecision than the conventional burr and laser based systems. Thevarious embodiments allow for a controlled delivery of precise volumesof the cooling fluids in selected portions of treatment areas, whileminimizing the interactions of the cooling fluid with the laser beam.The thin film may provide sufficient cooling while allowing asignificant portion of the laser beam energy to be absorbed in thematerial to be ablated.

In some embodiments, the cooling fluid is directed precisely into thecut area of the tooth while avoiding interference of the fluid with thelaser beam. This is particularly beneficial regardless of the type oflaser used, because as the cut deepens it usually becomes more difficultto get the cooling fluid into the cut area of the tooth, and it alsousually becomes difficult to minimize pooling of the coolant in the cutregion, and the pooled coolant can interfere significantly with thelaser beam. To this end, using one or more fluid controllers such asvalves, pressure switches, fluid flow switches, and pressure regulators,pumps, and nozzles, the form and amount of the coolant fluid present inthe region of treatment can be controlled such that the coolant fluidcan form a thin uniform film of the fluid on the area/region to betreated (e.g., a surface of a tooth), and such that the fluid does notpool into large drops. Treating the coolant fluid with surfactants canlower the surface tension of the fluid, which can reduce the undesirablepooling of the fluid. The use of a surfactant is beneficial if thecooling fluid, e.g., is water. In some embodiments, an additional nozzlecan provide an air curtain using a controlled flow of pressurized air,to reduce the likelihood that the coolant fluid may splash back afterhitting the tooth being treated. The air curtain system may be designedto provide a substantially laminar airflow so as to limit back splash ofthe cooling fluid.

Using an embodiment of a system and/or method that include one or moreof the above described features can lead to a high degree of control ofthe overall dental procedure, increasing the safety and comfort of thepatient. Together, a laser with a wavelength of about 5 to about 15 μmand a control system for regulating the coolant fluid delivery canenable an operator to cut precise user-defined patterns into the tooth.Thus, the fluid delivery control system provides to an operator (e.g. adentist) the ability to establish a cutting geometry that is best suitedto a particular tooth (i.e., shape, size, general health/condition ofthe tooth) and to the type of treatment.

FIG. 7 depicts an exemplary enamel/hard tissue ablation performancecurve. The volumetric removal rate is displayed on the Y-axis and thevolumetric flow rate of the coolant (e.g., a water air mist) isdisplayed on the X-axis. Near the Y-axis is a melting region 37 wherethe volumetric flow rate is low (typically less than 2 ml/min). Thevolumetric removal rates in the melting region is very low—generallyless than 20% of the optimized removal rate (e.g., about 0.25 mm³/s). Asthe volumetric flow rate of the coolant is increased (e.g., up to about3.5 ml/min), the temperature of the surface of the enamel/hard tissuedecreases and the undesired melting is eliminated or reducedsignificantly. When the surface melting is eliminated ablation dominatesand the enamel/hard tissue removal rate is maximized, e.g., about 0.25mm³/s, as shown at 38.

As the volumetric flow rate of the coolant is further increased (e.g.,up to about 7 ml/min), the enamel/hard tissue surface temperaturecontinues to stay below the melting point, so ablation continues. Butthe additional amount of coolant present in the treatment area/regionbegins to absorb increasing amounts of laser energy and, as such, theremoval rate begins to decrease. At a coolant flow rate of about 7ml/min, the removal rate drops to about 80% of the peak or optimizedremoval rate, as depicted at 39. As the volumetric flow rate continuesto increase (e.g., up to 20 ml/min) the coolant absorbs a large portionof the laser energy and an amount of laser radiation energy required tocause ablation is not absorbed in the enamel/hydroxyapatite. Thevolumetric removal rate decreases significantly as shown at 41 to about15% of the peak removal rate depicted at 38, and may remain low ordecrease further as depicted at 42.

With reference to FIG. 7, a change in laser energy is substantiallyprevented when the volumetric flow rate of the coolant fluid correspondsto the peak removal rate at 38. In contrast, the absorption of laserenergy by the hydroxyapatite is significantly affected if the flow rateof the coolant corresponds to the melting region and/or to the removalrates at 41, 42. The treatment efficiency (e.g., a percentage change inthe removal rate relative to the optimized removal rate) issignificantly attenuated in the melting region due to lack of adequatecooling. The treatment efficiency corresponding to the removal rates at39, 40 is attenuated, and corresponding to the removal rates at 41, 42is significantly attenuated, due to interference by the cooling fluidpresent in the treatment area/region. In general, cutting efficiency canbe expressed in terms of time required to perform the procedure, dentalmaterial removal rate, amount of melting occurred, quality of the cut interms of shape, fineness, etc., required skill to perform the cut, and acombination of two or more of these parameters. The cutting efficiencymay be controlled by adjusting one or more of the various parameterslisted in FIG. 5.

An exemplary cut in the enamel/hard tissue (about 2 mm×2 mm×2 mm involume) at differing coolant flow rates illustrates the effect excesscoolant may have on the efficiency of laser cutting. Cutting this volumeof enamel with a minimum of coolant flow rate without causing excessivemelting (about 3.5 ml/min) required on an average about 32 seconds andrequired a highly skilled operator to make a precise cut, in part, dueto the presence of debris and some melted enamel. This water flowsetting resulted in a material removal rate of about 0.25 mm³/s and isshown as 100% or peak rate 38 in FIG. 7. Cutting substantially the samevolume of enamel at a water flow rate of about 7 ml/min required about40 seconds. Cutting at this flow rate required less skill to make aprecise cut and the cut contained less debris and melt than that withthe flow rate of about 3.5 ml/min. The material removal rate at thisfluid flow setting was observed to be around 0.20 mm³/s and is shown inFIG. 7 at 39, as about 80% of the peak removal rate at 38. The removalof nearly the same volume of enamel/hard tissue at a coolant flow rateof about 9 ml/min required on an average about 44 seconds. The cutcontained even less amounts of melt and debris. This coolant flowsetting resulted in a material removal rate of about 0.18 mm³/s and canbe seen in FIG. 7 at 40, as about 72% of the peak removal rate at 38.

While the invention has been particularly shown and described withreference to specific embodiments, it will be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims. The scope of the invention is thusindicated by the appended claims and all changes that come within themeaning and range of equivalency of the claims are therefore intended tobe embraced.

What is claimed is:
 1. An apparatus for dental tissue treatment, theapparatus comprising: a laser source for generating a laser beam havinga wavelength in a range from 5 μm to 15 μm that is absorbed inhydroxyapatite in dental tissue; a system for directing the laser beamto an area of dental tissue to be treated; a controller for controllingthe laser beam; and a fluid-delivery system comprising a fluid flowswitch adapted to detect bubbles in a flow of a fluid comprising aliquid, the controller being adapted to automatically turn off the laserbeam in response to the fluid flow switch detection bubbles in the fluidflow, the fluid-delivery system being adapted for directing andcontrolling the flow of the fluid comprising the liquid to at least aportion of the area to be treated to substantially prevent a change inlaser energy absorption by the dental tissue and attenuation oftreatment efficiency due to fluid interference with the laser beam. 2.The apparatus of claim 1, wherein the fluid-delivery system isconfigured to adjust a rate of flow of the liquid.
 3. The apparatus ofclaim 1, wherein the fluid further comprises a gas.
 4. The apparatus ofclaim 3, wherein the fluid-delivery system is configured to adjust arate of flow of the gas.
 5. The apparatus of claim 3, wherein thefluid-delivery system is configured to adjust a pressure of the gas flowin the range from 0 psi up to 80 psi.
 6. The apparatus of claim 1,wherein the fluid-delivery system is configured to adjust a rate of flowof the fluid.
 7. The apparatus of claim 1, wherein the fluid-deliverysystem is configured to adjust a pressure of the fluid flow in the rangefrom 0 psi up to 80 psi.
 8. The apparatus of claim 1, wherein: thefluid-delivery system comprises a positive displacement pump forcontrolling the flow of the fluid; the pump operates at a frequency ofup to 750 rpm; and the frequency of the pump controls a rate of flow ofthe liquid.
 9. The apparatus of claim 8, wherein the positivedisplacement pump comprises a peristaltic pump.
 10. The apparatus ofclaim 1, wherein: the fluid is delivered using a nozzle forming aplurality of orifices.
 11. The apparatus of claim 10, wherein the nozzleforms up to 10 orifices.
 12. The apparatus of claim 10, wherein eachorifice of the plurality of orifices has a diameter in a range from0.008 inches up to 0.15 inches.
 13. The apparatus of claim 10, whereinthe plurality of orifices are disposed about a rim of the nozzle. 14.The apparatus of claim 1, wherein the dental tissue is a hard dentaltissue.
 15. A method for dental tissue treatment, comprising: generatinga laser beam having a wavelength in a range from 5 μm to 15 μm that isabsorbed in hydroxyapatite in dental tissue; directing the laser beam toan area of dental tissue to be treated; detecting bubbles in a fluidflow comprising a liquid using a fluid flow switch; turning off thelaser beam in response automatically with a controller; and directingand controlling the flow of the fluid comprising the liquid to at leasta portion of the area to be treated to substantially prevent a change inlaser energy absorption by the dental tissue and attenuation oftreatment efficiency due to fluid interference with the laser beam. 16.The method of claim 15, wherein a rate of flow of the liquid isadjusted.
 17. The method of claim 15, wherein the fluid furthercomprises a gas.
 18. The method of claim 17, wherein a rate of flow ofthe gas is adjusted.
 19. The method of claim 17, wherein a pressure ofthe gas flow is adjusted such that the pressure is in a range from 0 psiup to 80 psi.
 20. The method of claim 15, wherein a rate of flow of thefluid is adjusted.
 21. The method of claim 15, wherein a pressure of thefluid flow is adjusted such that the pressure is in a range from 0 psiup to 80 psi.
 22. The method of claim 15, wherein: the controlling theflow of the fluid comprises pumping the fluid using a positivedisplacement pump; the controlling the flow of the liquid comprisesoperating the pump at a frequency of up to 750 rpm; and the frequency ofthe pump controls a rate of flow of the liquid.
 23. The method of claim22, wherein the positive displacement pump comprises a peristaltic pump.24. The method of claim 15, wherein: the fluid is delivered using anozzle forming a plurality of orifices.
 25. The method of claim 24,wherein the nozzle forms up to 10 orifices.
 26. The method of claim 24,wherein each orifice of the plurality of orifices has a diameter in arange from 0.008 inches up to 0.15 inches.
 27. The method of claim 24,wherein the plurality of orifices are disposed about a rim of thenozzle.
 28. The method of claim 15, wherein the dental tissue is a harddental tissue.